关于resetlogs

RESETLOGS | NORESETLOGS This clause determines whether Oracle Database resets the current log sequence number to 1, archives any unarchived logs (including the current log),
and discards any redo information that was not applied during recovery, ensuring that it will never be applied. Oracle Database uses 

NORESETLOGS

 automatically
except in the following specific situations, which require a setting for this clause:

You must specify 

RESETLOGS

:

After performing incomplete media recovery or media recovery using a backup control file

After a previous 

OPEN

 

RESETLOGS

 operation
that did not complete

After a 

FLASHBACK

 

DATABASE

 operation

If a created control file is mounted, then you must specify 

RESETLOGS

 if
the online logs are lost, or you must specify 

NORESETLOGS

 if they are not
lost.

When you open the database with the 

RESETLOGS

 option, the database
performs the following actions:

Archives the current online redo logs (if they are accessible) and then erases the contents of the online redo logs and resets the log sequence number to 1.

For example, if the current online redo logs are sequence 1000 and 1001 when you open 

RESETLOGS

,
then the database archives logs 1000 and 1001 and then resets the online redo logs to sequence 1 and 2.

Creates the online redo log files if they do not currently exist.

Initializes redo thread records and online redo log records in the control file to the beginning of the new database incarnation.

More specifically, the database sets the redo thread status to closed, sets the current thread sequence in the redo thread records to 1, sets the thread checkpoint of each redo thread to the beginning of log sequence 1, chooses one redo log from each thread
and initialize its sequence to 1, and so on.

Updates all current datafiles and online redo logs and all subsequent archived redo logs with a new 

RESETLOGS

 

SCN

 and
time stamp.

Because the database does not apply an archived redo log to a data file unless the 

RESETLOGS

 

SCN

 and
time stamps match, the 

RESETLOGS

 requirement prevents you from
corrupting data files with archived logs that are not from direct parent incarnations of the current incarnation. The relationship among incarnations is explained more fully in the following section.

In previous releases, it was recommended that you back up the database immediately after the 

OPEN
RESETLOGS

. Because you can now easily recover a pre-

RESETLOGS

 backup
like any other backup, making a new database backup is optional. To perform recovery through 

RESETLOGS

 you
must have all archived logs generated after the most recent backup and at least one control file (current, backup, or created).

参考：
http://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_1004.htm#SQLRF00802 http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmrvcon.htm#BRADV1171